The present invention relates to a plasma processing apparatus wherein a semiconductor substrate, a glass substrate for a liquid crystal display and so on is etched, ashed or otherwise processed by a plasma generated by using a microwave.
A plasma generated by adding energy from outside to a reacting gas is widely used in a manufacturing process of an LSI, an LCD and so on. Especially in a process of dry etching, use of the plasma is an indispensable core technology. Generally, exciting means for generating the plasma uses either a microwave having a frequency of 2.45 GHz for example, or an RF (radio frequency) having a frequency of 13.56 MHz for example. The former has an advantage over the latter in that a plasma of a higher density can be obtained. However, in a plasma processing apparatus using the microwave, it was difficult to generate the plasma in a wide area and at a uniform density. Yet, because of the above-mentioned advantage that a plasma of a higher density can be obtained in such a plasma apparatus, there has been a requirement for an apparatus capable of processing a large size of the semiconductor substrate, the glass substrate for LCD and other materials. In order to meet the requirement, the applicant of the present invention proposed in Japanese Patent Application Laid-Open No. 62-5600 (1987), Japanese Patent Application Laid-Open No. 62-99481 (1987), and so on, a following apparatus:
FIG. 1 is a sectional side view of a plasma apparatus of the same type as disclosed in Japanese Patent Application Laid-Open No. 62-5600 (1987) and Japanese Patent Application Laid-Open No. 62-99481 (1987). FIG. 2 is a plan view thereof. A reactor 41 in the shape of a rectangular box is entirely made of aluminum. The reactor 41 has an upper opening sealed airtight by a seal plate 44 for introducing a microwave. The seal plate 44 is made of a dielectric such as silica glass or alumina, i.e. which is heat resistant, transmittable by microwaves, as well as having a small rate in dielectric loss.
The reactor 41 has an upper portion connected with and covered by a cover member 50 in the shape of a rectangular box. The cover member 50 has a ceiling portion attached with a dielectric plate 51. There is an air gap 53 between the dielectric plate 51 and the seal plate 44. The dielectric plate 51 is made of such a dielectric like as a fluororesin such as Teflon (registered trademark), a polyethylene resin, a polystyrene resin and so on, being formed into a plate having a substantially pentagon in the shape of a rectangle portion combined with a triangle portion, with an apex of the pentagon provided with a projected portion. The projected portion is inserted into a waveguide 61 connected to a circumferential surface of the cover member 50. The waveguide 61 is connected to a microwave generator 60. A microwave emitted from the microwave generator 60 is guided by the waveguide 61 into the projected portion of the dielectric plate 51.
As has been described above, the projected portion of the dielectric plate 51 has a base end continuing to the substantially triangular tapered portion 51a as viewed from above. The microwave entered from the projected portion reaches the tapered portion 51a, expands widthwise of the tapered portion, and propagates throughout the whole of the dielectric plate 51. Then, the microwave reflects on an end surface of the cover member 50 opposing the waveguide 61. The incident wave is superimposed on the reflected wave, forming a standing wave in the dielectric plate 51.
The reactor 41 has an inner space as a processing chamber 42. The processing chamber 42 has a circumferential wall formed with a through hole fitted with a pipe 45, through which a necessary gas is introduced into the processing chamber 42. The processing chamber 42 has a bottom wall having a center portion provided with a table 43 for placing a work W to be processed by the plasma. The table 43 is connected to a high frequency power source 47 via a matching box 46. Further, the bottom wall of the reactor 41 is formed with exhaust holes 48 so that an atmosphere inside the processing chamber 42 is exhausted from the exhaust holes 48.
By using the plasma apparatus of the above constitution, a surface of the work W can be etched according to the following steps: First, inner gas is exhausted from the exhaust holes 48, bringing the processing chamber 42 into a partial vacuum of a desired pressure. Then, the reactive gas is supplied through the pipe 45 into the processing chamber 42. Then, the microwave generator 60 is activated to generate a microwave, and the microwave is introduced through the waveguide 61 into the dielectric plate 51. When introduced, the microwave is allowed by the tapered portion 51a to expand uniformly within the dielectric plate 51, forming a standing wave within the dielectric plate 51. The standing wave forms a leakage electric field below the dielectric plate 51, which introduces through the air gap 53 and seal plate 44 into the processing chamber 42. In such a manner, the microwave propagates inside the processing chamber 42, generating the plasma within the processing chamber 42.
The table 43 is applied with a high frequency wave by the high frequency power source 47 via the matching box 46, so that a bias electric potential is generated. The bias electric potential draws ions within the plasma onto the work W at an accelerated speed to etch the surface of the work W. According to the above, if a diameter of the reactor 41 is increased for a capacity to process the work W having a large size, it is possible to uniformly introduce the microwave to all regions of the reactor 41. Therefore, a uniform anisotropic etching can be performed even to the large sized work W.
There is a problem however: As has been described above, according to the prior art plasma processing apparatus, in order to uniformly expand the microwave throughout the dielectric plate 51, there is provided the seal plate 44, as well as the tapered portion 51a formed as part of the dielectric plate 51 projecting horizontally from an edge portion of the reactor 41. Size of the tapered portion 51a is determined in accordance with the area of the dielectric plate 51, i.e. the diameter of the processing chamber 42. As a result, when the prior art plasma processing apparatus is to be installed, there is a problem that an extra horizontal space must be provided for housing the tapered portion 51a which projects out of a perimeter of the reactor 41.
On the other hand, there has been a trend to increase the size of the work W, and there is a requirement for the reactor 41 having an increased diameter. Further, at the same time, there is a requirement that such an apparatus should not demand for extra space for installation; in other words, the apparatus must be installed within as small space as possible. However, according to the prior art apparatus as described above, the size of the tapered portion 51a depends on the diameter of the reactor 41, and therefore if the diameter of the reactor 41 is increased, the size of the tapered portion 51a must be made accordingly longer. As a result, the requirements conflicted against each other, i.e. a demand for a plasma processing apparatus having an increased diameter of the reactor 41 yet capable of being installed within as small space as possible.
Further, according to the prior art plasma processing apparatus, the circumferential wall of the reactor 41 for example is earthed so as to serve as a earthed electrode for the table 43 which is applied with the high frequency wave. However, with such an arrangement, there is another problem in that the inner surface of the circumferential wall of the reactor 41 is hit and damaged by the ions from within the plasma, decreasing life of the reactor 41. Still further, when the circumferential wall of the reactor 41 is earthed, there is a possibility that there will not be enough bias electric potential generated on the surface of the table 43. In such a case, the ions will have poor directivity toward the work W, which could be lower processing characteristics such as anisotropy and so on.
The present invention is made under the above circumstances, and it is therefore an object of the present invention to provide a plasma processing apparatus capable of being built as compact as possible so as to be installed in a small space even if the diameter of the reactor is large, having an improved directivity of the ions toward the work, and capable of providing longer life of the reactor.
A plasma processing apparatus according to the present invention, in brief summary, has a following arrangement. Specifically, an electrode is provided facing a table on which a work is to be placed, and an annular sealing member for introduction of a microwave is provided outside the electrode. Further, an antenna for emitting the microwave into a container is provided facing the seal plate for introduction of the microwave.
A plasma processing apparatus according to a first invention comprises an antenna emitting a microwave; a container into which the microwave emitted from the antenna is to be introduced; a table being provided with the container, being connected to a power source for application of a high frequency wave, for placement of a work for plasma processing by the microwave introduced into the container; and an electrode being provided with the container, facing the table. The invention is characterized by that the container has a sealing member for introduction of the microwave, provided at a location surrounding an outer perimeter of the electrode; that the antenna is faced with the sealing member; and that the microwave emitted from the antenna is introduced into the container through the sealing member.
In such a plasma apparatus as according to the first invention, the antenna shaped in a ring or a Roman character C or otherwise and disposed to face the annular sealing member provided in the container (reactor) emits the microwave, which is introduced through the sealing member into the container, thereby generating a plasma. When the high frequency wave is applied to the table, with the electrode faced to the table serving as a earthed electrode, the plasma generated as described above is drawn to the work placed on the table.
It has become possible to enter the microwave into the antenna without expanding the microwave widthwise. Thus, the antenna does not have to extend out of the container. As a result, the plasma processing apparatus according to the present invention can have a horizontal dimension made as small as possible. In other words, the plasma processing apparatus according to the present invention uses the antenna for supplying the microwave, and therefore it becomes possible to uniformly supply the microwave by using a limited space. Further, the antenna is disposed to face the annular sealing member, making possible to uniformly introduce the microwave into the container.
On the other hand, the electrode faced to the table applied with the high frequency wave can be used as the earthed electrode. As a result, the ion within the plasma is prevented from hitting and damaging an inner circumferential wall of the container, increasing life of the container. Further, since it is possible to stably generate a bias electric potential in the table, the ions within the plasma are drawn onto the work substantially perpendicularly, making possible to improve processing characteristics such as anisotropy and so on.
A plasma processing apparatus according to a second invention is the plasma processing apparatus according to the first invention, characterized by that the electrode is made of a material of a silicon family.
In such a plasma processing apparatus as according to the second invention, when a gas of a fluorocarbon family (CxFy gas) is used as the reactive gas for etching a silicon oxide film for example, the CxFy gas is dissociated by the plasma to form fluorine molecules (F or F2), relatively decreasing an etching rate of the silicon oxide film to the etching rate of a resist. However, since the electrode is made of the material of a silicon family according to the a present invention, fluorine molecules will contact and catalyze with the electrode to form and vaporize as SiF4. Thus, the fluorine molecules are selectively removed. This improves an etching rate of the silicon oxide film to the etching rate of the resist, making possible to perform the etching at a high selectivity ratio. Further, the electrode made of a material of a silicon family has another advantage of reduced problem about contamination.
A plasma processing apparatus according to a third invention is the plasma processing apparatus according to the first or second inventions, characterized by that the electrode is connected to a path for introduction of a gas into the container, and formed with a hole for supply of the gas into the container.
In such a plasma processing apparatus as according to the third invention, the reactive gas is introduced into the container through the holes being formed in the electrode facing the table. The reactive gas diffuses radially in all regions of the circumferential wall of the container, as well as substantially uniformly. Thus, the work is processed substantially uniformly by the plasma. Further, the reactive gas supplied in the container stays for a longer time within the plasma, improving efficiency in use of the reactive gas.
A plasma processing apparatus according to a fourth invention is the plasma processing apparatus according to the third invention, characterized in that the path is provided with a space for diffusion of the introduced gas.
In such a plasma processing apparatus as according to the fourth invention, the reactive gas is introduced into the space provided with the path, where the reactive gas is diffused to become uniformity. Then, the uniformly reactive gas is released through the holes formed in the electrode into the container. This makes possible to uniformly introduce into the container the gas from a plurality of parts of the electrode. Thus, the work can be processed more uniformly by the plasma.
A plasma processing apparatus according to a fifth invention is the plasma processing apparatus according to any of first through fourth inventions, characterized by further comprising a device for controlling of a temperature of the electrode.
In order to improve the processing characteristics of the plasma processing, it is important to control the temperature of a part exposed to the plasma. From such a point of view, in the plasma processing apparatus according to the fifth invention, the processing characteristics can be improved by adjusting the temperature of the electrode by the device for controlling the temperature.
A plasma processing apparatus according to a sixth invention is the plasma processing apparatus according to any of the first through fifth inventions, characterized by further comprising a power source for applying a high frequency wave to the electrode.
In such a plasma processing apparatus as according to the sixth invention, the high frequency wave of approximately 13.56 MHz for example is applied to the electrode, so that a plasma is generated between the electrode and the table separately from the plasma generated by the microwave introduced from the antenna into the container. In such a way, even if a distance between the table and a region where the plasma is generated, i.e. a distance from the sealing member and the electrode to the table, is made short, the plasma diffuses adequately, becoming substantially uniform in the plane including the work. Thus, the plasma processing apparatus can have a smaller vertical dimension, whereas needed plasma processing can be performed quickly.
Further, it becomes possible to generate the abovementioned plasma separately from the plasma generated by the microwave introduced from the antenna to the container. Thus, it becomes possible to equalize plasma-processing speed in a center portion and in a perimeter portion of the work, by controlling the power of the high frequency wave applied to the electrode, without controlling the power of the microwave emitted from the antenna.
A plasma processing apparatus according to a seventh invention is the plasma processing apparatus according to any of the first through sixth inventions, characterized by that the antenna has a waveguide path for introducing the microwave, being formed in a annular shape, a C-shape or a spiral shape, and the waveguide path having a portion formed with a slit, facing the sealing member.
A plasma processing apparatus according to an eighth invention is the plasma processing apparatus according to the seventh invention, characterized in that the waveguide is embedded with a dielectric.
In such plasma apparatuses as according to the seventh and eighth inventions, the microwave introduced into the annular waveguide of the antenna propagates inside the waveguide as progressive waves travelling in opposite directions to each other, and then both progressive waves meet and superimpose each other to form a standing wave within the antenna. On the other hand, the microwave entered in the antenna having the waveguide path formed in the shape of C or spiral reflect on the end portion of the waveguide path to form a standing wave in the antenna. This standing wave makes flow in an inner wall of the antenna an electric current that becomes maximum at a predetermined interval. Since the wall on which the electric current flows is formed with the slit, an electric field is emitted from the slit to the sealing member. Specifically, the microwave is emitted from the antenna to the sealing member. The microwave transmits the sealing member to be introduced into the container, generating a plasma. Since the waveguide is formed in the shape of C or spiral, it is possible to supply the microwave uniformly to a needed region. Further, since the waveguide is made to emit the microwave from the slit, needed emission of the microwave becomes possible by varying the shape and the location of the slit.
Further, a wavelength of the microwave entered into the antenna is decreased by the dielectric by /{square root over ( )} (xcex5r) times of the wavelength (where, xcex5r is a relative dielectric constant of the dielectric). Therefore, if the diameter of the antenna is the same, the antenna stuffed with the dielectric has more locations at which the electric current running in the inner wall of the antenna becomes maximum, than the antenna not stuffed with the dielectric, making possible to provide a greater number of slits accordingly. Therefore, it becomes possible to introduce the microwave uniformly into the container. It is possible that the waveguide is provided with the slits facing the sealing member with the stuffed the dielectric. More specifically, it is possible that the antenna has a bottom surface entirely opened. In such a case, as has been described, the microwave propagating in the dielectric forms the standing wave, the leakage electric field of the microwave passes through the sealing member to be introduced into the container, as a result, it is possible to introduce the microwave uniformly into the container. 
A plasma processing apparatus according to a ninth invention is a plasma processing apparatus comprising: an antenna for emitting a microwave; a container into which the microwave emitted from the antenna is to be introduced; a table being provided with the container for placing a work for plasma processing by the microwave introduced into the container, and an electrode being provided with the container, being connected to an electrical power source for application of a high frequency wave, facing the table. This plasma processing apparatus is characterized by that the container has a sealing member provided at a location surrounding an outer perimeter of the electrode; that the antenna is faced with the sealing member; and that the microwave emitted from the antenna is introduced into the container through the sealing member.
In such a plasma processing apparatus as according to the ninth invention, by applying to the electrode a high frequency wave of a range approximately 13.56 MHz for example, it becomes possible to generate a plasma between the electrode and the table separately from the plasma generated by the microwave introduced from the antenna into the container. Thus, it becomes possible to equalize plasma-processing speed in a center portion and in a perimeter portion of the work, by controlling the power of the high frequency wave applied to the electrode, without controlling the power of the microwave emitted from the antenna.
Needless to say, the ninth invention may be combined with the second through eighth inventions in the same manner as is the first invention. Note should be made, however, that according to the ninth invention, the power source for applying the high frequency wave is connected to the electrode instead of the table. For this reason, if the sixth invention is to be combined with the ninth invention, the power source for applying the high frequency wave and for being connected to the table instead of the electrode is further included.